Spark theme vs Halo theme

Question

Hi - I tried the following in one of my mxml files in Flex SDK4.
<mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml" dropShadowEnabled="true" dropShadowColor="#EBE6E6"
     backgroundColor="#E8E5E5" width="280" alpha="1" borderColor="#8d8d8d" borderThickness="1" borderStyle="solid" cornerRadius="8" creationComplete="setPopMsg(),fireEvent()" >
It gave an error "The style 'borderThickness' is only supported by type 'mx.containers.Canvas' with the theme(s) 'halo'."
Should we use only Spark theme with Flex 4? What is the difference between Spark and Halo themes?  which is good? Also what is the equivalent of setting borderThickness in spark theme?

Answer 1

Now that most of Halo theme which we used do it by CSS is no longer valid, also if a application is using "Halo" theme then the application can't be simple changed to "Spark" theme withput considerable change to UI look and feel. Also simple thing like TitleWindow close button is now part of skinning if using "Spark" theme, This is no longer a property of s:TitleWindow unlike mx:TitleWindow, similarly header color  was simple in mx:Panel but in s:Panel we have to do a  programatic skining. I am not sure why Adobe decided to "hide" CSS style for all the component.
Anybody has any insight into ? It is much more difficult to change theme dynamically.
Also changing the default color of mx:ProgressBar with "Halo" was so easy but with mx:ProgressBar with "Spark" theme, we have write a custom skin just for the progress bar.
Thanks